1. Field of the Invention.
This invention relates to a chalcogenide glass material used as optical fibers capable of transmitting infrared rays, particularly the ray of 10.6 .mu.m in wavelength.
2. Description of the Prior Art.
Optical fibers have heretofore been made of materials based on silica glass. Silica glass, however, has a disadvantage in that it is capable of transmitting light having a wavelength of up to approximately 2 .mu.m, but it absorbs substantial amount of a ray having a longer wavelength owing to the lattice vibration. Accordingly, conventional optical fibers of the silica glass type cannot transmit, for example, a ray of 10.6 .mu.m in wavelength which corresponds to that from CO.sub.2 -laser beam used in laser surgery or laser welding. For this reason, in the past searches for a material which transmits rays having a wavelength in the range of from 2 .mu.m to 20 .mu.m was extensibly carried out. As a consequence, chalcogenide glass was found promising as a useful material in said wavelength range. Of the chalcogenide glasses, the selenium-based glass has its lattice-vibrational absorption in the long wavelength region exceeding 20 .mu.m and, hence, can transmit the CO.sub.2 -laser beam of 10.6 .mu.m in wavelength. However, upon examination of the optical absorption characteristics of a germanium (Ge)-selenium (Se) glass as a typical example of Se-based glass, it is seen that, as shown in FIG. 1 attached hereto, there exists a strong absorption at a wavelength of 12.8 .mu.m due to the vibration of Ge-O bond formed by the contamination with oxygen. The tail of this vibrational absorption extends to a wavelength of 10.6 .mu.m. Owing to this absorption, the temperature of Ge-Se glass is elevated, leading to an abrupt increase in the absorption by free electrons. As a consequence, optical fibers consisting of such a type of glass have an important defect of a large absorption loss so that it is not practically used.